The founder and CEO of Microsoft have each donated $100,000 to support Washington state's marriage equality law that is being challenged by a referendum vote this November.

Checks from Microsoft founder Bill Gates and CEO Steve Ballmer were delivered to Washington United for Marriage on Friday.

"It's going to make a tremendous difference," Zach Silk of Washington United for Marriage said to the Associated Press on Monday. "It's very important for us to have that broad support from business leaders and companies themselves."

In addition to the individual gifts from Gates and Ballmer, Microsoft Corporation has contributed $10,000 to the campaign to approve Referendum 74 and defend the state’s marriage equality law, according to public disclosure records. Last January, the company joined Nike, Starbucks, Alcoa, Google, and other globally competitive Northwest employers in endorsing the marriage equality legislation. The company issued a statement at the time that said, “Passing the bill would be good for our business and for the state’s economy.”

Asked about the campaign, a Microsoft spokesperson said, “We’ve clearly stated our support for marriage equality in Washington. The reasons for supporting the legislation that we articulated in January are the same reasons we support the referendum now. When we announced our support for the bill, we understood the very real possibility that it would be challenged at the ballot. Microsoft’s contribution to the campaign is our company supporting marriage equality legislation through one last step in the process.”

Microsoft does not comment on the contributions of its individual corporate leaders.

Other top gifts to the campaign from business leaders include $44,936 from Amazon retiree Jennifer Cast, $50,000 from SCAFCO president Larry Stone, and $10,000 from Justin Voskuhl of Facebook, according to Washington United for Marriage. More than 7,000 Washingtonians and hundreds of small businesses have supported the campaign.

A marriage equality law was passed and signed by Gov. Christine Gregoire, but antigay activists, including the National Organization for Marriage have stepped in to challenge the law. Referendum 74 was certified for the November ballot with 240,000 signatures gathered by antigay groups.